GREETINGS OF THE PROPHET, praise and peace be upon him H 864 "The Prophet, praise and peace be upon him, would repeat his phrases three times so that it's meaning was fully understood, and when he met a group of people he would greet them three times with the salutation." R 864 Bukhari with a chain up to Anas who related this.
852- وعن أنسٍ رضي الله عنه : أنَّ النَّبيَّ صلى الله عليه وآله وسلم كَانَ إِذَا تكلم بِكَلِمَةٍ أعَادَهَا ثَلاثَاً حَتَّى تُفهَمَ عَنْهُ ، وَإِذَا أتَى عَلَى قَوْمٍ فَسَلَّمَ عَلَيْهِمْ سلم عَلَيْهِمْ ثَلاَثاً . رواه البخاري . وهذا مَحْمُولٌ عَلَى مَا إِذَا كَانَ الجَمْعُ كَثِيراً .